Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Simulation-Experiment Parameter_
| Platform | IBM Quantum |
|---|---|
| Software Development Kit | Qiskit(2.1.1) |
| Noise parameters (amplitude damping noise, depolarizing noise) | (0.001,0.01) |
Comparison of the proposed CASQKA protocol with other protocols_
| Protocol | Quantum resource | Identity authentication function | Semi-quantum properties | Qubit efficiency (%) |
|---|---|---|---|---|
| Ref. [36] | Cluster states | No | Yes | 2.08 |
| Ref. [28] | Cluster states | No | Yes | 1.60 |
| Ref. [39] | Five qubit entangled states | Yes | No | 7.70 |
| Ref. [40] | Bell states | No | Yes | 6.70 |
| Ref. [25] | Bell states | Yes | No | 16.67 |
| Ref. [22] | Four-particle GHZ states | Yes | No | 53.33 |
| Ref. [49] | Single-particle states | Yes | No | 16.67 |
| Ref. [50] | three-particle GHZ-like states | No | Yes | 16.67 |
| Proposed protocol | W states | Yes | Yes | 2.43 |
Communication complexity comparison_
| Metric | Proposed protocol | Ref [5] |
|---|---|---|
| Quantum communication complexity | 30n qubits | n qubits |
| Classical communication complexity | 3n classical bits | ~0.5n classical bits |
| Total communication complexity | 33n bits | 1.5n bits |
| Qubit efficiency (η) | 3.03% | ~66.67% |
All operational scenarios of Bob, Charlie, and Dave_
| Case | Bob | Charlie | Dave | Protocol phase |
|---|---|---|---|---|
| 1 | CTRL | CTRL | CTRL | |
| 2 | CTRL | CTRL | SIFT | |
| 3 | CTRL | SIFT | CTRL | |
| 4 | CTRL | SIFT | SIFT | Security check |
| 5 | SIFT | CTRL | CTRL | |
| 6 | SIFT | CTRL | SIFT | |
| 7 | SIFT | SIFT | CTRL | |
| 8 | SIFT | SIFT | SIFT | Key agreement |
Variable-Meaning_
| IB, IC, ID | Bob/Charlie/Dave’s pre-shared identity bit strings (n bits) |
| KA, KB, KC, KD | Each party’s private key string (n bits) |
| SA, SB, SC, SD | The four-particle sequences of the W state are held by Alice, Bob, Charlie, and Dave, respectively. |
| VB, VC, VD | The n-bit outcomes of Z-basis measurements performed by Bob/Charlie/Dave at the SIFT positions. |
| The XOR of the measurement outcome with the identity string, | |
| VAB, AC, VAD | The classical bit string actually measured by Alice at the corresponding positions, used for comparison and verification. |
| The n-bit SIFT measurement results of Bob/Charlie/Dave in Case-8 used to conceal the private key the final 4-party shared key | |
| KAB, KAC, KAD | The key segments permuted by Alice using IB, IC, ID are sent to Bob/Charlie/Dave, respectively. |
Encoding rules_
| Quantum states | Classical bits |
|---|---|
| |0〉 | 0 |
| |1〉 | 1 |